1. Field of the Invention
The invention relates to a cetane number estimation method for estimating the cetane number of diesel engine fuels.
2. Description of the Related Art
In diesel engines, compression ignition of fuel injected from each fuel injection valve occurs a certain time after the injection, that is, there is a so-called ignition delay before the injected fuel is ignited. In order to improve the output performance of diesel engines and reduce the emissions from them, control apparatuses that control the operation parameters for controlling the diesel engine, such as the fuel injection timing and the fuel injection amount, in consideration of the ignition delays are widely used (Refer to Japanese Patent Application Publication. No. 2001-152948 (JP-A-2001-152948).
Meanwhile, the smaller the cetane number of the fuel used in a diesel engine, the longer the ignition delays. Therefore, in a case where the operation parameters for the engine control are set for fuel having a standard cetane number, for example, if the fuel tank is refueled with fuel having a cetane number smaller than the standard cetane number, such as winter fuel, the ignition timing of the fuel is further delayed and the combustion state deteriorates, causing misfires in some cases.
This problem can be prevented by correcting the operation parameters for controlling the engine operation based on the cetane number of the fuel actually injected into the combustion chambers. To perform such correction properly, the cetane number of fuel needs to be accurately estimated.